In oil well operations, self contained downhole tools on a wire line and powered by a D. C. battery pack are used for measuring pressure and temperature, and for obtaining and storing such pressure and temperature data in a memory on a real time basis. Other tools such as flow meters and gamma ray tools are also run on wire line and take measurements data in a battery operated tool where the measurements data are recorded in a memory on a real time basis. The data is collected over a period of time and correlated to a real time clock in the well tool. Such data provides significant information from which the production, production life and hydrocarbon reserves available can be estimated.
In some instances it is necessary or desirable to retrieve a well tool and output the collected data for analysis and to rerun the tool in the well bore to gather more data or operate under a different set of collection instructions which are input to the tool. One of the inherent problems of this situation is that it is necessary to disconnect the D.C. battery pack from the well tool which disables the real time clock so that the second run data obtained in the well bore may not be correlatable to the first run data on a real time basis. Another and perhaps more significant problem is the lack of accurate synchronization of the data on a real time basis with other tools.
Relevant prior patent art includes the following patents and the cited patents therein:
U.S. Pat. No. 4,033,186 issued 7/05/77 to Bresie
U.S. Pat. No. 4,161,782 issued 7/17/79 to McCracken
U.S. Pat. No. 4,763,259 issued 8/09/88 to Delatorre
U.S. Pat. No. 4,624,136 issued 11/25/86 to Delatorre
In the U.S. Pat. No. 4,763,259, the well tool therein is compartmentalized and the electronics for the system can be checked prior to operation by use of a voltage/current system. After collecting downhole data, the data can be output using the current/voltage system and new data instructions can be installed in the tool central processing unit (CPU). The system, however, requires either the battery pack or the sensors to be disconnected for data transmission. When the battery pack is disconnected, real time continuity in the internal CPU is lost and when the sensors are disconnected, there is no way to verify proper sensor operation or confirm proper connection when reconnection is made. Also, there is no way of determining after re-assembly if the sensors are functioning.
In seeking accuracy of the measurement data where more than one run of a tool is desired, it is preferable to not disturb any components of the system which might alter their response to measurement in the second run.